Associations between air pollution and common mental health disorders may show a need for policy change.
The first long term study of air pollution exposure and the incidence of anxiety and depression has been published this month, identifying a clear association.
Given the growing burden of anxiety and depression disorders as well as previous findings from short-term studies indicating impacts on mental health from pollutants, this UK study set out to observe the long-term effects of the air we breathe on a very large sample population.
Nearly 400,000 participants with no prior history of anxiety or depression were evaluated over an average of 10.9 years. Throughout the course of the study, over 13,000 participants were diagnosed with depression and almost 16,000 were diagnosed with anxiety.
Annual mean air pollution was estimated using concentration of air particulates, nitric oxide, and nitrogen dioxide at participants’ residential addresses using the land use regression model. Particulate matter was separated into two groups – PM2.5 were particulates with an aerodynamic diameter of 2.5 micrometres or less, and PM2.5-10 had an aerodynamic diameter of 2.5-10 micrometres.
Association curves created from the experimental data were non-linear, with a steeper curve at low exposure and a plateau at high levels of exposure. Interestingly, the association between PM2.5 and anxiety were higher in males than in females.
The mechanisms which contribute to this association are not fully understood, but researchers posited that olfactory receptor neurons exposed to air pollution may trigger a central nervous system response. Systemic circulation and the trigeminal nerve may also contribute to the inflammatory and oxidative stress response, and air particulates may induce the release of proinflammatory mediators, activate the hypothalamic pituitary adrenal axis, and damage the blood-brain barrier.
Previous studies have not been able to say with any certainty that the observed associations were due to pollution rather than other aspects such as socioeconomic factors. However, this study had access to detailed information about the participants and the contributing variables specific to each person. Given this, the extensive length of the study, and the large sample size, the results are a strong indication of an increased risk of anxiety and depression due to air pollution.
The level of air pollution in this study were well below the UK air quality standards, indicating that the accepted level of pollution may be too high, especially as many countries’ air quality already exceed the World Health Organisation’s 2021 guidelines for acceptable pollution levels.
Researchers described the current global ambient air pollution as an urgent public health priority and a major worldwide health issue. “The non-linear association may have important implications for policy making in air pollution control. Reductions in joint exposure to multiple air pollutants may alleviate the disease burden of depression and anxiety”.